1. Field of the Invention
The present invention relates to an apparatus and method of controlling a stepper motor, and more particularly, to an apparatus and method to variably control a driving current applied to the stepper motor according to a torque operated on the stepper motor.
2. Description of the Related Art
A stepper motor rotates by a fixed angle in every changed state of excitation in each phase of the motor by clock pulse signals, and suspends at a fixed angle if the state of excitation does not change. The stepper motor rotates by the fixed angle or by a fixed step according to inputted pulse signals.
FIG. 1 is a schematic block diagram illustrating a conventional apparatus to control a stepper motor.
As shown in FIG. 1, a controller 100 outputs to a driver 110 driving pulse signals for each phase to drive a stepper motor 120. The controller 100 also outputs to the driver 110 a control signal that applies a predetermined driving current according to a preset driving current setting value Vref to the stepper motor 120.
The driving current applied to the stepper motor 120 is usually determined with a predetermined additional current so as to prevent a rotor of the stepper motor 120 from stepping out. When the rotor of the stepper motor 120 starts rotating from a suspended state, it requires greater torque than is required to maintain its rotation after the stopper motor 120 has been running. Taking this into consideration, the driving current setting value Vref is set to be greater than required to start the rotor from the suspended state. Thus, the driving current applied to the stepper motor 120 is usually more than actually required to drive the stepper motor 120.
The driver 110 drives the stepper motor 120 with the predetermined driving current according to the control signal outputted from the controller 100.
As the conventional apparatus to control the stepper motor 120 is configured so that the predetermined additional current for a magnitude of a rotary torque is applied to prevent the rotor of the stepper motor from stepping out, the rotor reaches a target position with repeated overshoot and settling in every step. Therefore, the conventional apparatus incurs problems of vibration, noise and resonance due to the additional driving current for an extra torque of the rotor, and also incurs problems of inaccurate operations of an overheated control IC (controller) and the stepper motor.